Extreme pressure lubricants containing diesters of chlorendic acid



EXTREME PRESSURE LUBRICANTS CONTAINING DIESTERS F Amos Dorinson, Park Forest, 111., assignor to Sinclair Refining Company, New York, N. Y., a corporation of Maine No Drawing. Application July 28, 1955,

' Serial No.

2 Claims. or. 252 54 5 This invention relates to new metal-working oil compositions consisting essentially of a mineral oil and a diester of chlorendic acid inwhich the ester groups contain from 4-to 8 carbon atoms. i I

Extreme pressure lubricants or cutting oils are employed to carry off excess heat and to lessen friction during metal cutting operations. Cutting oil compositions usually comprise a mineral oil base and an 'additive'which imparts a high film strength to the oil making it possible to maintain a lubricating film between the cutting tool and the metal being worked during the cutting operation. Additives which have been employed to impart extreme pressure properties to mineral oils frequently have undesirable properties such as unpleasant odors and toxicity. Examples of extreme pressure additives commonly incorporated in petroleum lubricating oils to provide cutting oils, include sulfurized lard oil, sulfurized sperm oil, sulfurized pincne, s ulfurized olefin polymers, sulfur-chlorinated sperm oil, sulfur-chlorinated pinene, sulfur-chlorinated mineral oil, chlorinated paraffin wax and chlorinated naphthalene among others. I

The present invention is particularly concerned with cutting oils used in breaching, gear cutting, hobbing planing and similar operations in which metal is removed from the work piece at a comparatively low rateQe. g. at cutting speeds of 10 to surface feet per minute. The metal chips removed vary in' thickness from 0.005 to 0.0005 inch. A major objective of cuttingoperations of this type is the achievement of a good surface finish, and, therefore, one of the functions of a cutting oil for use in such operations is to improve the surface finish obtained.

Certain short chain chlorinated compounds such as carbon tetrachloride, ethylene dichloride and diisobutylene dichloride are known tobe especially effective as additives for broaching and gear cuttingd oils. Although an excellent surface'fini'sh can be obtained onwork"p'ieces by the inclusion of carbon tetrachloride in broaching and gear cutting oils, this compound is not suitable as a cutting oil additive for two reasons. Firstly, due to the volatility of carbon tetrachloride, it is rapidly lost by evaporation from the cutting oil during use, thus necessitating close control of the concentration and frequent replenishment with fresh carbon tetrachloride. Secondly, carbon tetrachloride is a toxic substance which causes severe physiological damage when inhaled as a vapor or when absorbed through the skin by contact. Ethylene dichloride is also highly volatile. Diisobutylene dichloride, which might be used as a substitute for carbon tetrachloride due to its lack of toxicity, is objectionable because of its highly unpleasant odor which could not be tolerated for the length of an average working day. Therefore, a need exists in the art for a non-toxic, nonvolatile, substantially odorless, mineral oil-soluble additive which imparts high pressure properties to a cutting oil composition.

It has now been found that metal-working oils having extreme pressure properties suitable to allow the fabrica- 2,771,423 ia n d Nav- 0 ,5

tion of work pieces with desirable smooth surface finishes can be prepared by dissolving a diester of chlorendic acid in a lubricating oil medium. The oil soluble esters of chlorendic acid are those formed by esterifying both of the carboxyl groups'of the acid with alcohols having from 4 to 8 carbon atoms in the molecule to obtain a compound of the formula in which R and R" represent the hydrocarbon residues of the alcohols. These diesters of chlorendic acid, unlike the short chain chlorinated compounds referred to above, are not volatile at room temperature and have no odor. In' addition to these advantages, feeding tests on laboratory animals have shown derivatives of chlorendic acid to be non-toxic. The diesters ofchlorendic acid in which the ester groups each contain from 4 to 8 carbon atoms are readily prepared, easily handled, liquids which are miscible with mineral oils in all proportions. Therefore, cutting oil compositions containing the chlorendic acid di'esters can be prepared by a simple blending operation. Thediestrs canhave the same or a different number of carbon atoms in'the two ester groups so long as each estergroup contains at least 4 carbon atoms. The corresponding esters, which have fewer than 4 carbon atoms in the ester groups, such as the dimethyl and diethyl esters of chlorendic acid are solids which are unsuitable for use in the present invention. The mono esters of chlorendic acid, chlorendic acid itself and chlorendic anhydride are alsounsuitable for use in the present invention. The preferred additive of the present invention is dibutyl chlorendate.

The smoothness of the surface of a work piece produced with the cutting oil compositions of this invention depends, among other factors, on the percentage of diester in the composition. It has been found that about 10 to percent of the diester, based upon the weight of the cutting oil composition, produces a satisfactory surface in cutting operations on most metals without rendaring the compositions obnoxious or toxic to the user or subject to loss of chlorine by vaporization.

' The preparation of the additives used in the cutting oil compositions of the present invention is illustrated by the following example.

' EXAMPLE 1 Dibutyl chlorendate was prepared from 371 grams of chlorendic anhydride (1 mole), 300 grams of n'butanol (4- moles) and 2.5 grams of p-toluene sulfonic acid. The reactants were refluxed until the theoretical amount of water (18 cc.) had been collected in a Dean-Stark water trap. The excess butanol was then removed under a vacuum of 2 to 20 mm. at a pot temperature of C. The product, dibutyl chlorendate, had an acid number of 1.99 (theoretical 0.0), a saponification number of 227 (theoretical 224) and a chlorine analysis of 42.0% (theoretical 42.5%).

The diester can also be prepared as above from chlorendic acid by removing 2 moles of water for each mole of ester formed. The other diesters of chlorendic acid useful in the present invention are prepared by the above procedure substituting the appropriate alcohol for butanol, for example, n-amyl alcohol, iso-amyl alcohol, hexyl' alcohol, heptyl alcohol or octyl alcohol. The water of reaction may be removed azeotropically by distillation with a solvent such as benzene or toluene. The preparation of the diester of chlorendic acid forms no part of the present invention and, therefore any other suitable method of preparation may be employed.

The dibutyl chlorendate prepared in the above example contained a small amount of residual chlorendic acid due to incomplete esterification. Tests were conducted to determine whether or not the desirable properties of the product were due to the presence of the small amount of unreacted acid. The surface finishes obtained on two steels with two cutting oils are compared in Table I below. One oil contained 25 percent of dibutyl chlorendate with an acid number of 2 while the other cutting oil contained the same amount of dibutyl chlorendate with an acid number of 0. The two sets of figures agree within experimental error indicating that the effect of the small amount of the unreacted acid is negligible.

The advantages to be obtained by using the cutting oils of the present invention become apparent in cases where the surface finish requirements for the work piece are unusually stringent. be cut satisfactorily when the root-mean-square surface roughness in microinches, lies within the range from 50 to 70. In certain cases, however, it is required to produce gears for which the upper limit of root-mean-square surface roughness is 50 microinches, a roughness of 40 microinches or less being preferred. As is pointed out above, the smoothness of the finish obtained on the work piece depends, among other factors, upon the amount of chlorendic acid diester present in the cutting oil compositions. The amount of diester required to produce a given quality of surface also varies with the type of metal being worked. For illustration, it has been found that when dibutyl chlorendate is used as an additive in cutting oils, the provision of at least about 14 percent of the diester achieves an acceptable surface in cutting operations on most steels. For some steels, to percent of dibutyl chlorendate is required to produce a surface finish of 50 microinches whereas a surface finish of 40 microinches might require from to percent of dibutyl chlorendate in the cutting oil. For most steels used in the manufacture of gears, 50 percent of dibutyl chlorendate in the cutting oil represents the maximum effective concentration and no advantage would be obtained by the use of higher concentrations. However, with certain types of steel, for exam- Ordinarily, a gear is considered to ple, AISI 1045, the surface finish can be improved by increasing the concentration of dibutyl chlorendate in the cutting oil above 50 percent. Therefore, it is seen that the amounts of the dibutyl ester which should be present in cutting oil compositions to produce a surface of high quality in operations of the type for which the present compositions are designed, ranges from about 14 percent to somewhat more than 50 percent of dibutyl chlorendate for practical purposes, although as much as percent or more of the diester might be required in unusual cases. More specifically, it has been found that a cutting oil composition containing about 22 to 35 percent of dibutyl chlorendate, based on the weight of the composition, produces a surface finish in the 40 to 50 microinch range on AISI 8620 and AMS 6260 steels whereas a larger percentage of dibutyl chlorendate (43 percent) is required to produce a 50 microinch finish on AISI 4150 steel. Therefore, the use of dibutyl chlorendate or any of the other diesters contemplated by the present invention allows the preparation of stable non-toxic cutting oils suitable for use where the quality requirements of the work piece are exacting.

It is to be understood that the specific examples given above are for illustrative purposes only and are not to be construed as limiting the scope of the present invention which contemplates the use of the defined diesters of chlorendic acid in mineral oil base cutting oil compositions in amounts sufiicient to impart the desired high pressure properties to the compositions.

I claim:

1. A metal-working oil composition consisting essentially of mineral oil and a diester of chlorendic acid in which the ester groups contain from 4 to 8 carbon atoms; the amount of diester present constituting about 10 to 75 percent of the composition by weight and being sufficient to impart extreme pressure properties to the composition.

2. A metal-working oil composition consisting essentially of mineral oil and dibutyl chlorendate; the amount of dibutyl chlorendate present constituting at least about 14 percent of the composition by weight and being sufficient to impart extreme pressure properties to the composition.

References Cited in the file of this patent UNITED STATES PATENTS 2,635,979 Lidov Apr. 21, 1953 2,645,614 Holmes June 14, 1953 2,733,248 Lidov Jan. 31, 1956 v FOREIGN PATENTS 1,053,043 France Sept. 30, 1953 OTHER REFERENCES Prill: J. Am. Chem. Soc., 69, 62-63 (1947). 

1. A METAL-WORKING OIL COMPOSITION CONSISTING ESSENTIALLY OF MINERAL OIL AND A DIESTER OF CHLORENDIC ACID IN WHICH THE ESTER GROUPS CONTAIN FROM 4 TO 8 CARBON ATOMS; THE AMOUNT OF DIESTER PRESENT CONSTITUTING ABOUT 10 TO 75 PERCENT OF THE COMPOSITION BY WEIGHT AND BEING SUFFICIENT TO IMPART EXTREME PRESSURE PROPERTIES TO THE COMPOSITION. 